Plasma processing system and apparatus and a sample processing method

ABSTRACT

A plasma processing apparatus includes a processing chamber, a sample bench in the processing chamber mounting a wafer thereon, a plate having a plurality of through holes including discharge holes through which a processing gas flows into the processing chamber, the plate being disposed in an upper portion of the processing chamber, and a member in the upper portion of the processing chamber and provided with the plate on the side thereof facing the plasma. A light receiving unit is provided having an optical transmitter for transmitting therethrough a light from inside of the processing chamber having passed the through holes formed in the plate. The light receiving unit is attached to the member, and an end face of the optical transmitter is opposed to a back of the plate and the through holes so as to be in contact therewith or spaced therefrom by a minute gap.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This is a continuation of U.S. application Ser. No. 09/788,463,filed Feb. 21, 2001, the subject matter of which is incorporated byreference herein and is copending with U.S. application Ser. No.10/732,285, filed Dec. 11, 2003 and U.S. application Ser. No.10/732,286, filed Dec. 11, 2003.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a plasma processing system and asample processing method, and particularly to a plasma processing systemand sample processing method suited for forming a fine pattern in thesemiconductor production process. It relates more particularly to anapparatus or a sample processing method to measure plasma emission in aprocess chamber and the state of thin film on the surface of such asample as wafer.

[0004] 2. Related Background Art

[0005] A plasma processing apparatus is extensively used in the fineworking phase such as etching, film formation and ashing of thesemiconductor production process. In the plasma processing apparatus,the process gas introduced into a vacuum chamber (reactor) is convertedinto plasma by a plasma generating means, and is made to react on thesurface of a semiconductor wafer to provide such treatment as processingof fine holes and grooves or film formation. Furthermore, the requiredtreatment is provided by discharging volatile reaction products

[0006] In this plasma processing apparatus, attempts have been made todetect the end point of the etching process by detecting the radiationfrom plasma during processing, and to measure the film thickness andetching/film forming rate from the reflective light and interferencesignal on the thin film of wafer surface for plasma radiation in realtime, thereby improving the plasma processing accuracy. For example,Official Gazette of Japanese Patent Laid-Open NO. 136098/1993 disclosesa parallel plate plasma etching system where two or more plasmareceiving sensors are installed on the surface of the electrode oppositeto the wafer, and uniform plasma density is ensured by obtaininginformation on the rate, film thickness uniformity and distribution fromplasma radiation strength at multiple points of the wafer.

[0007] Official Gazette of Japanese Patent Laid-Open NO. 148118/1991discloses a parallel plate plasma etching system where laser beam isapplied to the wafer from the upper position through a top plateelectrode, and the volume of etching is measured through the reflectedlaser beam, thereby detecting the end point. To avoid contamination ofthe top electrode according to said Gazette, this system has a hole witha diameter of about 10 mm formed on the portion of the quartz-madeelectrode cover where laser beam passes, and measures the volume ofetching with high accuracy without laser beam being damped even if theelectrode cover is contaminated; this ensures stable detection of an endpoint.

[0008] The methods described above, however, have the followingproblems: For monitoring of the state of thin film or the like on thewafer surface, it is preferred to measure from the upper positionopposite to the wafer or from the upper position at an angle of about45°. The plasma processing apparatus which allows measurement in such amanner is restricted in the measurement method and structure. In themicrowave ECR method and inductively coupled plasma processingapparatus, for example, a quartz-made transparent window and plate maybe installed above the wafer in order to apply microwaves inside theprocess chamber or to introduce inductive electric field. In this case,the state of the wafer surface can be measured from above. However, inthe so-called capacitatively coupled parallel plate plasma processingapparatus, the top electrode opposite to the wafer is made of conductivemetal such as aluminum, so it is not structured to allow the surface ofthe wafer to be directly penetrated. For this reason, measurement of thewafer surface requires a sensor for a plasma radiation to be installedon the surface of the electrode opposite to the wafer, as indicated inthe Official Gazette of Japanese Patent Laid-Open NO. 136098/1993.However, reaction products are deposited on the sensor for a plasmaradiation according to repeated electric discharges. This makes it verydifficult to ensure stable measurement for a long time.

[0009] One of the attempts to solve this problem is the method disclosedin the Official Gazette of Japanese Patent Laid-Open NO. 148118/1991. Ahole having a diameter of about 10 mm is formed on the measurementportion of the quartz-made electrode cover directly exposed to plasmawhere laser beam passes, thereby eliminating an adverse effect onmeasurement, despite the deposit membrane formed on the quartz-madecover surface. However, this method does not ensure stable measurement.To get the specified plasma density required for plasma processing,high-frequency power amounting to several kilowatts of high power isapplied to the top electrode. If an about 10 mm-diameter hole is formedon the electrode and electrode cover as disclosed in said OfficialGazette, local abnormal discharge will occur to the hole, or plasma willenter the hole, and the top electrode and electrode cover may bedamaged. Furthermore, bias is applied to the top electrode, the topelectrode will be sputtered by ions in plasma through the hole on theelectrode cover. Since the top electrode is made of such a metal asaluminum, it may be damaged or entry of particle contamination mayresult.

[0010] Needless to say, the wafer surface can be measured in principlefrom the side wall of the process chamber at a smaller inclination,instead of from the upper position opposite to the wafer. However, anopposite plate type where such a plate as silicon is placed opposite tothe sample at a position several tens of millimeters away is oftenadopted especially in the oxide film etching system, in order to controlexcessive dissociation of process gas and to improve processreproducibility. In this case, the angle of measuring the wafer has tobe about 10° in practice. It is also difficult to ensure satisfactorymeasuring accuracy. Under these circumstances, it has been hoped thatthe state of wafer surface can be measured from the top opposite to thewafer in the opposite plate type plasma processing apparatus as well.

[0011] With reference to the microwave ECR system and inductivelycoupled plasma processing apparatus, authors of the present inventionhave described that wafer surface can be measured from a quartz-madetransparent window above the wafer. However, reaction products aredeposited on the quartz-made window surface as discharge is repeated,and transmittance is reduced. Conversely, surface is etched and is maderough, so stable measurement for a long time is difficult. For thisreason, this system has failed to meet practical requirements.

SUMMARY OF THE INVENTION

[0012] The present invention has been made to solve said problems. It isintended to provide a plasma processing apparatus and a sampleprocessing method which ensure stable measurement of the sample surfaceand plasma state from the external vacuum chamber or the wall state ofthe vacuum chamber with high accuracy for a long time, without abnormaldischarge or occurrence of particle contamination.

[0013] Authors of the present invention have studied the above problemsfrom the view point of ensuring practicability and reliability, and havefound out the following solutions:

[0014] The present invention provides a plasma processing apparatuswherein process gas is supplied into a vacuum chamber, plasma isgenerated by a plasma generator and a sample placed on a sample bench isprocessed by said plasma; said plasma processing apparatus furthercharacterized in that

[0015] an optical reflector is arranged within said vacuum chamber,

[0016] at least one or more through-holes with depth-to-diameter ratiosranging from 5 up to 100 are formed at a position opposite to saidoptical reflector of said vacuum chamber, and

[0017] a means of measuring optical information from the surface stateof said optical reflector via said through-hole is provided.

[0018] The present invention is characterized in that a plasmaprocessing apparatus wherein process gas is supplied into a vacuumchamber, plasma is generated by a plasma generator and a sample placedon a sample bench is processed by said plasma, provides;

[0019] an optical reflector which is arranged within said vacuumchamber,

[0020] at least one or more through-holes with depth-to-diameter ratiosranging from 5 up to 100 which are formed at a position opposite to anoptical reflector of said vacuum chamber and on a structure in contactwith said plasma,

[0021] an optical transmitter which is installed on the back of saidthrough-hole so that one end face thereof will be almost in contact withsaid structure,

[0022] an optical transmission means which is laid out on the other endface of said transmitter, and

[0023] a means of measuring optical information from the surface stateof said optical reflector via said optical transmitter and said opticaltransmission means.

[0024] The present invention is further characterized in that thediameter of said through-hole is 0.1 mm to 5 mm, desirably 0.3 mm to 2mm.

[0025] The present invention is still further characterized in that thetotal of the opening area of said through-hole is made 5 to 50% of thetotal area of the area in which a plural of said through-holes areformed.

[0026] A further characteristic of the present invention is that quartzor sapphire is used as said optical transmitter.

[0027] A still further characteristic of the present invention is thestructure which enables easy replacement of said optical transmitter byremoving one set of holding means and vacuum sealing means which holdssaid optical transmitter in position, when said vacuum chamber isreleased to the atmosphere.

[0028] The present invention is still further characterized in that aplasma processing apparatus wherein process gas is supplied into avacuum chamber, plasma is generated by a plasma generator and a sampleplaced on a sample bench is processed by said plasma, provides;

[0029] an optical reflector which is arranged within said vacuumchamber,

[0030] at least one or more through-holes with depth-to-diameter ratiosranging from 5 up to 100 which are formed at a position opposite to anoptical reflector of said vacuum chamber,

[0031] a means of measuring optical information from the surface stateof said optical reflector via said through-hole, and

[0032] a means of determining whether some foreign substance hasgenerated, based on the variations of said optical information.

[0033] The present invention is still further characterized in that aplasma processing apparatus wherein process gas is supplied into avacuum chamber, plasma is generated by a plasma generator and a sampleplaced on a sample bench is processed by said plasma, provides;

[0034] an optical reflector which is arranged within said vacuumchamber,

[0035] at least one or more through-holes with depth-to-diameter ratiosranging from 5 up to 100 which are formed at a position opposite to anoptical reflector of said vacuum chamber and on a structure in contactwith said plasma,

[0036] a means of measuring optical information from the surface stateof said optical reflector via said through-hole, and

[0037] a means of determining to what extent said structure has beenconsumed, based on the variations of said optical information.

[0038] The present invention is still further characterized in that asample processing method whereof process gas is supplied into a vacuumchamber, plasma is generated by a plasma generator and a sample placedon a sample bench is processed by said plasma, is performed to processsaid sample while;

[0039] measuring optical information from the surface state of saidsample via at least one or more through-holes with depth-to-diameterratios ranging from 5 up to 100 which are formed on the wall of saidvacuum chamber at a position opposite to said sample of said vacuumchamber, and while

[0040] measuring the state of the thin film on the surface of saidsample based on the variations of said optical information.

[0041] According to the present invention, the plasma processingapparatus is so designed as to provide an optical reflector which isarranged within the vacuum chamber, at least one or more through-holeswith depth-to-diameter ratios (aspect ratio) ranging from 5 up to 100which are formed at a position of a vacuum chamber opposite to anoptical reflector, and a means of measuring optical information from thesurface state of said optical reflector via said through-hole. So theplasma processing apparatus cannot reduce light transmissioncharacteristics due to adhesion of reaction productions on the end faceof an optical transmitter even if making repeated discharge for a longperiod of time.

[0042] Furthermore, the through-hole diameter is so small and aspectratio is so large that plasma cannot enter internal through-holes togenerate abnormal discharge.

[0043] What is more, if the quartz or sapphire having an excellent lighttransmittance and great resistance against plasma is used as an opticaltransmitter, deterioration of optical performance due to the damage onthe end face of the optical transmitter can be sufficiently reduced,thereby ensuring a stable measurement for a long time.

[0044] In addition, sample surface and plasma radiation can be measuredwith sufficient sensitivity and accuracy by compact arrangement ofmultiple through-holes with an exposed area ratio of 5 to 50%.

[0045] What is more, the down time in wet cleaning of the plasmaprocessing apparatus can be minimized by adoption of the structurepermitting easy replacement of an optical transmitter 141. This preventsthe availability factor of the plasma processing apparatus from beingreduced.

[0046] In addition, if reaction productions, causing occurrence ofparticle contamination, which have accumulated at the periphery of thesusceptor or on the sidewall inside the vacuum chamber, peel off fromthe optical reflector, changing a quantity of light from the opticalreflector takes place. So detecting this change enables a warning to begenerated for the purpose of prevention of frequent occurrence ofparticle contamination. This warning leads to decide a proper time ofcleaning out the internal plasma processing apparatus, enabling toprevent abnormality from occurring during operation of the plasmaprocessing apparatus.

[0047] Furthermore, monitoring a quantity of radiation measured with thethrough-hole on the plate leads to detect consumption of the plate,enabling to prevent abnormality from occurring during operation of theplasma processing apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

[0048]FIG. 1 is a schematic diagram representing the cross section ofthe plasma etching apparatus as an embodiment of the present invention;

[0049]FIG. 2 represents the through-hole section as a major portion ofthe present invention;

[0050]FIG. 3 represents one embodiment of through-hole arrangementaccording to the present invention;

[0051]FIG. 4 represents another embodiment of through-hole arrangementaccording to the present invention;

[0052]FIG. 5 represents a dependency of the aspect ratio to the solidangle of the through-hole of the present invention;

[0053]FIG. 6 represents an example of a experimental signal in theembodiment.

[0054]FIG. 7 is a drawing used to explain an example using an imageforming optical system as another embodiment according to the presentinvention;

[0055]FIG. 8 is a drawing used to explain operations in the embodimentof FIG. 6;

[0056]FIG. 9 represents an example of using a hollow structure in theoptical transmitter as another embodiment according to the presentinvention;

[0057]FIG. 10 is a drawing to explain an example of diagnosing theapparatus by installing a reflector on the susceptor or on the sidewallof the vacuum chamber;

[0058]FIG. 11 is a sectional view of a gas effluence port to explain anexample of diagnosing the apparatus with respect to consumptiondetection of the plate for supplying gas in other embodiments of thepresent invention; and

[0059]FIG. 12 is a drawing to explain the changes in emission and solidangle in the embodiment of FIG. 11.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0060] The following describes the embodiments according to the presentinvention with reference to the drawings:

[0061]FIG. 1 shows an embodiment where the present invention is appliedto the magnetic field UHF band electromagnetic wave radiation/dischargetype plasma etching apparatus. It is a cross sectional view of saidplasma etching apparatus in schematic form.

[0062] The process chamber 100 in FIG. 1 is a vacuum vessel providing avacuum of about 10⁻⁶ Torr. An antenna 110 which emits electromagneticwave as a plasma generating means is provided on the top thereof, and abottom electrode 130 to mount such sample W as wafer is installed on thebottom thereof. Antenna 110 and bottom electrode 130 are installed inparallel opposite to each other. A magnetic field forming means 101consisting of an electromagnetic coil and yoke, for example, isinstalled around the process chamber 100 to provide a magnetic fieldhaving a specified distribution and strength. Process gas introducedinto the process chamber is made into plasma by interaction between theelectromagnetic wave radiated from antenna 110 and magnetic fieldproduced by the magnetic field forming means 101, and plasma P isgenerated to treat the sample W on the bottom electrode 130.

[0063] Vacuum exhaustion and pressure control of process chamber 100 isprovided by the vacuum exhaust system 104 connected to vacuum chamber103 and pressure control means 105, and the internal pressure can becontrolled to a specified value, for example, within the range from 0.5Pa to 4 Pa. The process chamber 100 and vacuum chamber 103 provideground potential. The side wall 102 of process chamber 100 has itstemperature controlled, for example, to 50° C. by a temperature controlmeans (not illustrated).

[0064] Antenna 110 radiating electromagnetic waves consists of a diskformed conductor 111, dielectric 112 and dielectric ring 113, and isheld by a housing 114 as part of the vacuum vessel. Furthermore, a plate115 is installed on the surface of the disk formed conductor 111 on theside in contact with plasma. Process gas used to provide sample etchingand film formation is supplied at a specified flow-rate and mixing ratiofrom the gas supply means 116. It is made uniformed inside the diskformed conductor 111 and is supplied to the process chamber 100 throughnumerous holes provided on plate 115. The temperature of the disk formedconductor 111 is controlled , for example, to 30° C. by a temperaturecontrol means (not illustrated). The antenna 110 is connected throughthe incoming end 126 to antenna power supply system 120 comprising anantenna power supply 121, antenna bias power supply 123 and matchingcircuit/filter systems.122, 124 and 125. The antenna power supply 121supplies the UHF frequency power preferably in the range from 300 MHz to900 MHz to radiate UHF band electromagnetic waves through the antenna110.

[0065] The antenna bias power supply 123 applies to the plate 115 thebias of a frequency of, for example, 100 kHz or several MHz to severaltens of MHz through the disk formed conductor 111, thereby controllingthe reaction on the surface of plate 115. Especially in the oxide filmetching process using CF based gas, reaction of F radical and CFxradical on the surface of the plate 115 can be controlled and thepercentage of radicals can be adjusted by using high purity silicon andcarbon as the material of plate 115. In the present embodiment, theplate 115 is made of highly pure silicon. Aluminum is used as materialfor the disk formed conductor 111 and housing, and quartz is used forthe dielectric 112 and dielectric ring 113. Distance between the bottomof the plate 115 and wafer W (hereafter called “gap”) is 30 mm to 150mm, or preferably 50 mm to 120 mm. In the present embodiment, thefrequency of the antenna power supply 121 is 450 MHz, and that ofantenna bias power supply 122 is 13.56 MHz; gap is set at 70 mm.

[0066] A bottom electrode 130 is mounted opposite to the antenna 110 onthe bottom of the process chamber 100. A sample W such as wafer ismounted on the top surface of the bottom electrode 130, namely, on thesample mounting surface, and is held in position by an electrostaticchucking unit 131. On the peripheral area of the sample W, a samplebench ring 132 made of highly pure silicon, for example, is mounted onthe insulator 133. A bias power supply 134 to supply bias electric powerpreferably in the range from 400 kHz to 13.56 MHz is connected to thebottom electrode 130 through matching circuit/filter system 135, therebycontrolling the bias applied to sample W. In the present embodiment, thefrequency of the bias power supply 134 is 800 kHz.

[0067] The following describes the measuring ports 140A and 140Binstalled to measure the state of the surface of the sample W as a majorportion in the present embodiment. In the present embodiment, measuringports 140A and 140B are mounted on the antenna 110 opposite to thesample W. As will be described later, the state of thin film on thesurface of the sample W can be measured from the top in the verticaldirection through numerous through-holes formed on plate 115.Information on distribution inside the surface of the sample W can beobtained by placing the measuring port 140B at the position where theperipheral portion of the sample is measured, and by mounting themeasuring port 140A at the position intermediate between the peripheralportion and the center of the sample W. It goes without saying that theposition for installation of the measuring port is not restricted to twopositions; peripheral and intermediate positions, as described justabove. The measuring port can be installed at one position or threepositions. Or other arrangement may be used; for example, the port maylaid out on the circumference.

[0068] For example, optical transmission means 151A and 151B such as theoptical fiber and lens are provided on the measuring ports 140A and140B. Optical information reflecting the surface state of the wafer Wsuch as light directly coming from the plasma P or reflected light orinterference light on the wafer W surface of the plasma P is sent, forexample, to the camera and interference thin film gauge or measuringinstrument 152 consisting of the image processing apparatus, wheremeasurement is performed. The measuring instrument 152 is controlled bythe measuring instrument control/operation means 153, and is connectedto a higher-order system. The system control means 154 monitors andcontrols the state of the equipment and system through the controlinterface 155.

[0069] The plasma etching apparatus according to the present embodimentis configured as described above. The following describes a specificprocess to etch the silicon oxide film, for example, using this plasmaetching apparatus:

[0070] Firstly, wafer W as an object for treatment is fed into theprocess chamber 100 from a sample introduction mechanism (notillustrated). It is then mounted and chucked on the bottom electrode130, and the height of the bottom electrode is adjusted as required. Thegap is then adjusted to a specified value. Vacuum-exhausting is made bythe vacuum exhaust system 106 inside the process chamber 100. Meanwhile,gases required for sample W etching treatment, for example, C₄F₈, Ar andO₂ are fed into the process chamber 100 from the plate 115 of theantenna 110 from the gas supply means 116 at a specified flow rate andmixing ratio (for example, Ar at the rate of 400 sccm, C₄F₈ at the rateof 15 sccm and O₂ at the rate of 5 sccm). At the same time, the pressureinside the process chamber 100 is adjusted to a specified processingpressure: for example, it is adjusted to reach 2 Pa. Meanwhile, almosthorizontal magnetic field of approximate 160 gausses corresponding tothe electronic cyclotron resonant magnetic field strength for frequencyof 450 MHz of the antenna power supply 121 is formed close to the bottomof the plate 115 by the magnetic field forming means 101. The UHF bandelectromagnetic wave is radiated from the antenna 110 from the antennapower supply 121, and plasma is generated inside the process chamber 100by interaction with magnetic field. Process gas is dissociated by thisplasma P to generate ion and radical. Furthermore, antenna radiofrequency power supply 123 and bias power supply 134 are controlled toprovide the wafer W with such treatment as etching.

[0071] For example, electric power of antenna power supply 121 is 1000watts, that of antenna radio frequency power supply 123 is 300 watts,and that of the bias power supply 134 is 800 watts. Supply of electricpower and process gas is terminated upon termination of etching. Thenetching process completely terminates.

[0072] The optical information reflecting the state of plasma radiationand wafer surface during this treatment is transmitted by the opticaltransmission means 151A and 151B through the measuring ports 140A and140B, and is measured by the measuring instrument 152. The operation isprocessed by the measuring instrument control/operation means 153 basedon the result of measurement. Then the result is transmitted to thehigh-order system control means 154, and the plasma processing apparatusis controlled through the control interface 155.

[0073] The following describes the detailed structure of the measuringport 140 with reference to FIGS. 2 to 4:

[0074]FIG. 2 is an enlarged cross sectional view representing theportion of the measuring port 140 mounted on the antenna 110 in theembodiment shown in FIG. 1. As described with reference to FIG. 1, thedisk formed conductor 111 and dielectric 112 forming the antenna 110 areheld by the housing 114, and a plate 115 is installed on the disk formedconductor 111. Numerous gas permeation holes 115A are provided on theplate 115. In the disk formed conductor 111, process gas is fed into theprocess chamber 100 through gas permeation hole 111A located at theposition corresponding to that of gas permeation hole 115A. The gaspermeation hole 115A provided on the plate 115, for example, is athrough-hole having an approximate diameter of 0.1 mm to 5 mm,preferably, 0.3 mm to 2 mm. The gas permeation hole 111A provided on thedisk formed conductor 111 is equal to or greater in size than the hole115A; for example, it has an approximate of diameter of 0.5 mm to 5 mm,preferably, 2 mm. Approximate thickness of the plate 115 is 3 mm to 20mm. According to the present embodiment, it is 6 mm.

[0075] Numerous closely packed through-holes 115B are formed on theportion of the plate 115 corresponding to measuring port 140, andoptical transmitter 141 is installed almost in contact with the back ofthe plate 115 (on the surface opposite to the plasma P). It isvacuum-sealed with the housing 114 by the holding means 142 and vacuumsealing means 143 such as an O-ring and is mounted in position. Suchoptical transmission means 151 as an optical fiber and lens, forexample, are provided on the end face of the optical transmitter 141 onthe atmospheric side. Light 145P directly coming from the plasma P,reflected light from the surface of the sample W of the plasma P, andinterference light 145W pass through the through-hole 115B of the plate115 such as the optical path 144 indicated by a broken line, and reachesthe optical transmission means 151 through the optical transmitter 141.They are then sent to the measuring instrument 152, where measurement isperformed.

[0076] As described later, the aspect ratio of through-hole 115B ispreferred to range approximately 5 and more through within 100.

[0077] According to this embodiment, the optical transmitter 141 is madeof a quartz-made cylindrical rod. The suitable diameter of the opticaltransmitter 141 is 5 mm to 30 mm. The present embodiment uses a diameterof 10 mm. Similarly to the gas permeation hole 115A, the diameter of thethrough-hole 115B is 0.1 mm to 5 mm, or preferably 0.3 mm to 2 mm. Thediameter of the present embodiment is 0.5 mm. Multiple through-holes115B, or several tens of them are preferred to be installed to improvethe measuring sensitivity. As will be described below, this embodimentuses about 40 holes.

[0078]FIG. 3 represents one embodiment of the layout of through-holes115B. In this embodiment, about 40 through-holes 115B are arranged at apitch of 1.5 mm in the area corresponding to the end face of the opticaltransmitter 141 so that a regular triangle is formed at an equallyspaced interval. As described above, the diameter of the through-hole115B is 0.5 mm in this embodiment. The exposed area ratio (percentage ofthe total apertures of the through-hole 115B for the area of the endface of the optical transmitter 141) is about 10% (=(0.5²(mm²)×40)/(10²) (mm²)). This can provide a sufficient measuringsensitivity. It goes without saying that the through-hole arrangement isnot restricted to FIG. 3 alone. For example, these holes can be laid outso that they will cross one another, as shown in FIG. 4. Or they can belaid out in concentric arrangement. As suggested, holes can be laid outin various arrangements.

[0079] Some space (1 mm or more, for example) must be provided betweenadjacent through-holes. So the exposed area ratio will be reduced as thethrough-hole diameter is smaller. For example, if holes having adiameter of 0.3 mm are to be laid out at a pitch of 1.3 mm (a width of 1mm between apertures) in the area having a diameter of 10 mm, theexposed area ratio is about 5%. Measurement is also possible when theexposed area ratio is about 5%. For in-situ measurement of etching rateand others, the exposed area ratio is preferred to be about 5% or more.So from the view point of measurement sensitivity, the through-holediameter is preferred to be about 0.3 mm or more. Meanwhile, thediameter of the through-hole 115B is preferred to be set sufficientlysmaller than the mean free path of the molecule, as will be describedlater. In order not to allow abnormal discharge to take place, thethrough-hole diameter is 0.1 mm to around 5 mm, or is preferred to be0.3 mm to around 2 mm.

[0080] If the through-hole 115B diameter is made the same as that of gaspermeation hole 115A, there is an advantage that the cost increase canbe controlled without increasing the number of processing steps of plate115. It goes without saying that the hole diameters need not always bemade the same. The optimum value can be set according to the sensitivityand stability in measurement. Furthermore, all the diameters of thethrough-holes 115B need not be made the same. For example, the holediameter may be larger on the periphery.

[0081] The optical transmitter 141 need not be completely “transparent”,namely, it need not be transmissive in the entire visible light area.Only a sufficient transmittance is required in the wavelength area to bemeasured. For example, use of quartz or sapphire is preferred to measurefrom 200 nm ultraviolet area to 800 nm near-infrared area holding thevisible light area in-between. Silicon or such an optical material asZnS which provides excellent transmittance in the infrared area can beused to measure in the infrared area. Furthermore, a thin film of Al₂O₃such as sapphire, for example, may be formed on the end face of theoptical transmitter 141 in order to improve resistance to ion sputterand to reduce reflection factor.

[0082] The measuring port 140 has the configuration described above.This configuration avoids abnormal discharge, occurrence of particlecontamination or deterioration of optical performance such astransmittance at the measuring port 140, and ensures stable measurementfor a long time. The following describes the reasons:

[0083] If a hole having a diameter of about 10 mm is formed on the topelectrode, local abnormal discharge will occur to the hole due to thehollow cathode or plasma will enter the hole to damage the interior, asreferred to above as a problem of the prior art. By contrast, thethrough-hole diameter is set to as small as 0.5 mm in the presentembodiment. This does not allow abnormal discharge to occur in thethrough-hole or the plasma to enter the through-hole. After experiments,the present inventors have verified that measurement can be made withoutabove-mentioned abnormal discharge by setting the diameter of thethrough-hole 115B to about 5 mm or less, or more preferably to about 2mm or less. Furthermore, the optical transmitter 141 is installed at theposition almost in contact with the back of the through-hole 115B;therefore, there is no space between the through-hole 115B and opticaltransmitter 141 which may allow abnormal discharge to occur. Thus,abnormal discharge does not occur in this position, either.

[0084] The present embodiment ensures stable measurement for a long timewithout reaction product depositing on the end face of the opticaltransmitter 141, or transmittance being deteriorated by repeateddischarge.

[0085] This is because the diameter of the through-hole 115B is set at avalue sufficiently smaller than mean free path of molecules, in thefirst place. Working pressure in the process chamber is about 0.5 Pa to4 Pa. The mean free path of molecules in this case is about 5 mm to 30mm (Ar molecule at 25° C.). For this, the diameter D_(h) of thethrough-hole 115B is about 0.5 mm, so the ratio with the mean free pathof the molecule λ, namely, the value of D_(h)/λ is about D_(h)/λ=0.02 to0.1. As has been described, the diameter D_(h) of the through-hole 115Bis set at a value sufficiently smaller than the mean free path of themolecule: thus, the possibility is very small that gas molecule inplasma P enters the through-hole 115B.

[0086] Secondly, the diameter of the through-hole 115B is 0.5 mm in thepresent embodiment. By contrast, depth as a plate thickness is set at 6mm. As described above, the aspect ratio (=depth/diameter) is 10 or moreand the hole has a sufficient depth. So the probability of the radicalpassing through the through-hole 115B and depositing on the end face ofthe optical transmitter 141 is kept at a sufficient small rate.

[0087] The possibility of which the radical accumulates on the end faceof the optical transmitter 141 is proportional to solid angle dΩ makingallowance of the through-hole 115B (hole diameter: D, length: L) on theend face. FIG. 5 shows dependency of the aspect ratio (AR=L/D) of solidangle dΩ. The solid angle dΩ is inversely proportional to the square ofAR, as shown in FIG. 5. If the solid angle dΩ is aspect ratios of 5 andmore, the solid angle dΩ is below 1/100 of solid angle π on the planesurface. So the possibility of the radical reaching onto the end face ofthe optical transmitter 141 is kept at a sufficient small rate. In orderto get impurity prevention effect on the end face of the opticaltransmitter 141, the aspect ratio of the through-hole 115B is preferredto range from 5 to 100.

[0088] In addition, the plate 115 is heated by plasma, and the surfacetemperature rises to 100° C. or more. So the possibility of reactionproduct depositing inside the through-hole 115B is small. Deposits donot attach and grow inside the through-hole 115B to reduce the actualtransmission area of the through-hole.

[0089] Thirdly, bias voltage of several tens of volts to hundreds ofvolts is applied to the plate 115; therefore, ion in plasma will bedrawn toward the depth of the through-hole 115B. Thus, ion having anenergy of several tens of eV to hundreds of eV may reach the end face ofthe optical transmitter 141, although this probability is low. So evenif reaction products have deposited on the end face of the opticaltransmitter 141, they will be removed quickly by the ion sputteringeffect. Optical performance due to damaged end face of the opticaltransmitter 141 can be reduced sufficiently by manufacturing the opticaltransmitter 141, for example, with the quartz or sapphire which ishighly resistant to plasma.

[0090] The following can be said as an overall result of these effects:The optical transmitter 141 does not have reaction products deposited onthe end face or the surface roughened, and light transmission is keptconstant, despite repeated discharge. This ensures stable measurementfor a long time.

[0091] Regarding above-mentioned three factors, authors of the presentinvention have continued experimental studies, and have verified thatstable measurement can be made without abnormal discharge by setting thethrough-hole diameter to 0.5 mm and plate thickness to 6 mm, withrespect to the case where the oxide film on the surface of example W issubjected to etching processing, as explained in the present embodiment.FIG. 5 is a schematic diagram of the signal waveforms gained in thepresent experiment. Interference signals resulting from changes ininterference due to light reflected from the oxide film surface andunderlying layer are obtained with the progress of etching treatment.In-situ measurement of the etching rate is possible from this cycle. Inaddition, plasma emission signal as light directly coming from plasma isalso gained. These interference signals and plasma emission signals arechanged simultaneously at the end point of the etching processing. It isclear that the state of the surface and changes of plasma composition atthe end point of the etching processing can be detected. These signalscan be detected with sufficiently high precision over at least severaltens of hours of discharge. Furthermore, the number of particlecontamination having occurred during this time does not exceed 20 (0.2microns or more). Thus, stable measurement has been confirmed.

[0092] As can be seen from FIG. 2, the optical transmitter 141 is heldand is vacuum sealed by the holding means 142 and vacuum sealing means143 alone. This allows easy replacement by removing the holding means142 when the process chamber is released to the atmosphere.Consequently, if deposits are gradually accumulated on the end face ofthe optical transmitter 141 or the surface is roughened by ionsputtering, depending on process conditions, then easy replacement ofthe optical transmitter 141 is possible when wet cleaning is made byreleasing the plasma processing apparatus to the atmosphere. Thisminimizes the down time at the time of wet cleaning (complete cleaning).

[0093] Using FIGS. 6 and 7, the following describes another embodiment,the detection optical system which provides measurement through thethrough-hole 115B. In the embodiment shown in FIG. 2, the opticaltransmission means 151 is made of an optical fiber. Light 145P directlycoming from plasma P located in the middle of the optical path 144, andreflected light and interference light 145W on the surface of sample Wof plasma P all enter the optical fiber for measurement. Especially whenradical components in plasma are changed with the progress of etchingprocessing, this arrangement is suited to detect such a change.Meanwhile, for sensitive detection of the change in the state of surfacesuch as thickness of a thin film of sample W, light directly emittedfrom plasma P forms a noise component for measurement. So failure of itsdetection may be preferable to the measuring system. In such cases, animage forming optical system using a lens or the like is preferably usedfor the optical system.

[0094]FIG. 7 shows one embodiment of such an optical system. In thepresent embodiment, the optical transmission means 151 uses a lens 151Aas an image forming means. Optical information from the surface of thesample W is made to form an image on the detecting element 152A of themeasuring instrument 152 such as the camera and image processingapparatus. Light 145P directly coming from plasma P is cut off byarranging the filter 152B including the diaphragm and pin holeimmediately before the detecting element 152A. Only the opticalinformation 145W from the surface of sample W can be transmitted to thedetecting element 152A. This improves the sensitivity of detection andmeasurement of the state on the surface of sample W.

[0095] In the present embodiment, a through-hole 115B is located at somemidpoint in the optical system. It may appear difficult to measure thesurface of sample W because the optical path is cut off. However, whenthe aspect ratio (=depth/diameter) of the through-hole 115B is set to anappropriate value in relation to the expansion of light from the surfaceof sample W, measurement is possible without the through-hole 115Bcutting off the optical path.

[0096] This will be described in greater details with reference to FIG.8. FIG. 8 is a schematic diagram showing only the portion related to themeasurement and optical system of the embodiment shown in FIG. 7. Thefollowing shows the symbols in the Figure.

[0097] D_(h): Diameter of through-hole 115B

[0098] L_(h): Depth of through-hole 115B (equal to the thickness ofplate 115)

[0099] L_(g): Distance between sample W and plate 115 (equivalent to gapdescribed in embodiment of FIG. 1)

[0100] L_(z): Distance from sample W to image forming means 151A

[0101] (L_(z)-L_(g) is equivalent to thickness of antenna portiondescribed in embodiment of FIG. 1)

[0102] D_(z): Effective diameter of image forming means (lens accordingto the present embodiment) 151A

[0103] (almost equivalent to the diameter D_(r) of optical transmitter141)

[0104] As already described, each of the actual values in the presentembodiment is as follows: D_(h)=0.5 mm (diameter), L_(h)=6 mm, L_(g)=70mm and D_(r)=D_(z)=10 mm (diameter). Furthermore, the thickness ofantenna portion is L_(z)−L_(g)=80 mm, so L_(z)=150 mm.

[0105] Here the divergence angle θ from the surface of sample W isexpressed by θ_(z)=tan−1 ((D_(z)/2)/L_(z)), based on ratio L_(z)/D_(z)between distance L_(z) of the image forming means 151A from the sample Wand effective diameter D_(z). In the present embodiment, θ_(z)=1.9°.L_(z)/D_(z) equivalent to the divergence angle of beam from the surfaceof sample W is about 15. By contrast, prospective angle θ_(h) based onthe aspect ratio L_(h)/D_(h) of the through-hole 115B is defined asθ_(h)=tan−1 ((D_(h)/2)/L_(h)); then θ_(h)=2.3°. This value is a littlesmaller than θ_(z)=1.9°. As described above, if the beam divergenceangle θ_(z) from the surface of sample W is set to a value a littlesmaller than the prospective angle θ_(h) of the through-hole 115B, beamfrom the surface of sample W will reach the image forming means 151Awithout being cut off by the through-hole 115B, and will form an imageon the detecting element 152A.

[0106]FIG. 8 shows how this was verified by experiment. Image Img1 of acharacter of several mm square was depicted on the surface of sample W.The surface of sample W was observed during plasma processing. Then itwas found out that Image Img1 was optically transmitted to the surfaceof sample, and image Img2 is displayed on the display screen 152C ofmeasuring instrument 152. This image Img2 was slightly affected on itsperiphery by the eclipse resulting from by the through-hole 115B(expressed by the broken line in concentric circle in FIG. 8), butinformation on the original image Img1 is sufficiently retained. It hasa sufficient quality to measure the state of thin film on the surface ofsample W. Oxide film of the surface of sample W was subjected to etchingprocessing by plasma P. Then interference signals due to light reflectedfrom the oxide film surface and underlying layer were obtainedcorresponding to changes in the thickness of oxide film according to theprogress of etching treatment, similarly to what was shown in FIG. 6.This experimentally verified that in-situ measurement of the etchingrate is possible.

[0107] Incidentally, the embodiments mentioned above use the opticaltransmitter 141 made of a quartz-made rod. This is only one example. Itgoes without saying that other arrangements are also possible. Thefollowing describes another embodiment with reference to FIG. 9. FIG. 9shows the arrangement where the rod as an optical transmitter 141 wasmade hollow with its interior removed, and an optical fiber was insertedtherein as an optical transmission means 151. In FIG. 9, a gas supplier111B is provided on the portion corresponding to the through-hole 115Bof the disk formed conductor 111. So even under the process conditionswhere reaction products are likely to deposit on the end face of theoptical transmitter 141, it is possible to prevent reaction productsfrom depositing since process gas is also supplied from gas supplier111B. What is more, the optical path for the light passing through theoptical transmitter 141 can be shortened as shown in FIG. 9. This hasthe effect of reducing loss of optical information.

[0108] Next, description will be made of the embodiment of detecting thechange of a quantity of reaction productions, causing the occurrence ofparticle contamination, accumulating at the periphery of the susceptorand on the sidewall inside the vacuum chamber, with reference to FIG.10. This description will be omitted of the identical parts to those inFIG. 1. The optical reflectors 169A and 196B are installed on thesidewall of the insulator 133 covering the susceptor or on the sidewallinside the vacuum chamber 102. A measuring port 160A or 161A having thethrough-hole of the present invention is installed at a positionopposite to these reflectors. Measurement is made by transmitting thechange of reflected or interfered light from the reflectors to anoptical measuring instrument 162 via the optical transmission means 161Aor 161B. The optical measuring instrument 162 is controlled by ameasuring instrument control means and calculation means 163. Whenmeasured amount of reflected or interfered light has changedsubstantially, a display means 164 issues a warning.

[0109] According to this embodiment, if reaction productions, causingoccurrence of foreign substance, which have accumulated at the peripheryof the susceptor or on the sidewall inside the vacuum chamber, peel offfrom the optical reflector, changing a quantity of light from theoptical reflector takes place. So detecting this change enables awarning to be generated for the purpose of prevention of frequentoccurrence of foreign substance. This warning leads to decide a propertime of cleaning out the plasma processing apparatus, enabling toprevent abnormality from occurring during operation of the plasmaprocessing apparatus.

[0110] Next, description will be made of the embodiment of detectingconsumption of the plate 115 for diagnosing the system during acontinuous etching processing, with reference to FIG. 11 and FIG. 12.

[0111] High frequency power is applied to the plate 115 through theantenna power supply 121 during wafer-etching processing, so the plateis etched and consumed. FIG. 11 shows the processing-time dependency ofthe cross section of gas effluence port 115A on the plate 115. As shownin FIG. 11, longer time of etching processing decreases the thickness ofthe plate and increases the diameter of the hole on the vacuum chamberside. When further etching processing is continued, the gas effluenceport 115A becomes a through-hole of approximately 4.5 mm in thicknessand of approximately 1.3 mm in hole diameter. Such a gas effluence portincreases area by 10.6 times in initial etching processing. So thismakes a supply state of etching gas change significantly, makes abnormaldischarge induce in the gas effluence port, or makes occurrence offoreign substance more possible, causing a serious damage to continuousetching processing.

[0112] In FIG. 12, the solid line represents changes in solid angle dΩ,which are disposed under the shape of gas effluence port. In addition,the changes in a quantity of radiation at this time are given by markingsome black circles. FIG. 12 shows that a solid angle dΩ does notindicates a great change within 400 hours of processing time, but itincreases rapidly when processing time exceeds 500 hours. It is alsofound that the changes in a quantity of radiation has a similartendency. This proves that, when processing time exceeds 500 hours, thismakes more possible occurrence of a serious damage to continuous etchingprocessing.

[0113] According to this embodiment, monitoring a quantity of radiationmeasured through a measuring port with the through-hole of the presentinvention detects consumption of plate 115, enabling to preventabnormality from occurring during operation of the plasma processingapparatus.

[0114] All of said embodiments have referred to the magnetic field UHFband electromagnetic wave radiation/discharge type plasma processingapparatus. However, for example, 2.45 GHz microwave or VHF band waveranging from several tens of MHz to 300 MHz in addition to the UHF bandwave can be radiated as electromagnetic wave. Magnetic field strengthhas been explained for the case of 160 gausses which signify electroniccyclotron resonant magnetic field strength for 450 MHz. The resonantmagnetic field need not necessarily be used; a stronger magnetic fieldor weak magnetic field on the order of several tens of gausses or moremay be used. Furthermore, it goes without saying that the presentinvention can also be applied to capacitatively coupled parallel plateplasma processing apparatus and magnetron type plasma processingapparatus or inductively coupled plasma processing apparatus, inaddition to electromagnetic wave radiation/discharge type plasmaprocessing apparatus.

[0115] The structure of the upper plate opposite to the wafer iscomparatively simple especially in the plasma processing apparatus whereradio frequency is applied to the bottom electrode and a ground plate ismounted on the top. This makes it easy to install a measuring portsimilar to that of the present invention. Furthermore, in the parallelplate plasma processing apparatus where radio frequency is applied tothe top electrode to generate plasma, several kilowatts of high powerradio frequency is applied to the top electrode. So abnormal dischargecan occur if a hole or void is provided on the top electrode. Accordingto the structure of the present invention, however, abnormal dischargeor other failure does occur to the measuring port. Especially in thenarrow electrode type parallel plate plasma system, the space betweenthe top and bottom electrodes is small, and so it is very difficult toget from the side the information on the wafer surface and the plasmabetween top and bottom electrodes. This indicates that the presentinvention provides considerable advantages.

[0116] Meanwhile, in the inductively coupled plasma processing apparatus(ICP), the state of wafer surface can be measured to some extent when atransparent quartz is used for the top plate. The measuring portaccording to the present invention can be applied when an alumina-madedome and silicon plate or the like is used. To put it more specifically,those skilled in the art can easily design the arrangement wheremultiple closely packed holes are formed on an alumina-made plate or thelike as shown in FIG. 3, and a vacuum sealing quartz plate is installedon the back. In the ICP type plasma processing apparatus, the top platemay have to be heated to a high temperature of 150° C. or more, forexample, in order to get the process characteristic and reproducibility.It goes without saying that the present invention is applicable evenunder such temperature conditions.

[0117] The object to be treated was a semiconductor wafer in each ofsaid embodiments, and etching of the semiconductor wafer was mentioned.However, the present invention is not restricted to them. For example,the present invention is also applicable when the object for treatmentis a liquid crystal substrate. In addition, treatment is not restrictedonly to etching. For example, the present invention is also applicableto sputtering and CVD treatment.

[0118] As described above, the present invention ensures a stable and along-term measurement of the state of the sample surface and plasma orthe state of the wall of the vacuum chamber with high accuracy from theexternal vacuum chamber, without allowing abnormal discharge or particlecontamination to occur.

[0119] For example, the present invention ensures a stable and precisionmeasurement of the state of thin film of the plasma and sample surfacefrom above the sample W or from the upwardly inclined position for along time even on a mass production level, in the opposite plate typestructure where the antenna and electrode are installed opposite to thewafer surface, without allowing abnormal discharge or particlecontamination to occur. As a result, it enables detection of the endpoint in etching process and in-situ monitoring of etching/film formingrate and uniformity. Thus, the present invention permits a more advancedprocess control and improves reproducibility of treatment and stabilityin treatment, and provides a plasma processing apparatus contributing toimprovement of the apparatus availability factor and productivity.

What is claimed is:
 1. A plasma processing apparatus comprising: aprocessing chamber in which an inside thereof is evacuated; a samplebench which is located in a lower portion of the processing chamber andon which a wafer to be processed is placed; a plate having a pluralityof through holes including discharge holes through which a processinggas flows into the processing chamber, the plate being disposed in anupper portion of the processing chamber in opposition to the wafer; anda member which is situated in the upper portion of the processingchamber and provided with the plate on a side thereof facing the plasma,wherein electric power for forming an electric field in the processingchamber is supplied to the plate and a plasma is generated between thewafer and the plate; and a light receiving unit having an opticaltransmitter for transmitting, therethrough a light from the inside ofthe processing chamber having passed the through holes formed in theplate, the light receiving unit being attached to the member situated inthe upper portion of the processing chamber, and an end face of theoptical transmitter being opposed to a back of the plate and the throughholes so as to be one of in contact therewith and spaced therefrom by aminute gap.
 2. A plasma processing apparatus according to claim 1,wherein the light receiving unit is attached to the member and is sealedthereto.
 3. A plasma processing apparatus according to claim 1, whereinthe member disposed in the upper portion of the processing chamber is aflat plate member which is disposed in parallel with the wafer beingopposed thereto.
 4. A plasma processing apparatus according to claim 3,wherein the light receiving unit is attached being to the member and issealed thereto.
 5. A plasma processing apparatus comprising: a vacuumchamber; a sample bench which is located in a lower portion inside ofthe vacuum chamber and on which a wafer to be processed is placed; aplate which is situated in an upper portion inside of the vacuum chamberso as to be opposed to the wafer and is supplied with electric power forforming an electric field in the vacuum chamber; and a plurality ofthrough holes including discharge holes formed in the plate throughwhich a processing gas flows into the vacuum chamber, a plasma beinggenerated between the plate and the wafer; a member which is situated inthe upper portion of the vacuum chamber and provided with the plate onthe side thereof facing the plasma; and a light receiving unit having anoptical transmitter for transmitting, therethrough a light inside of thevacuum chamber having passed the through holes penetrating the plate,the light receiving unit being attached to the member situated in theupper portion of the vacuum chamber, and an end face of the opticaltransmitter being opposed to the back of the plate and the through holesso as to be one of in contact therewith and spaced therefrom by a minutegap.
 6. A plasma processing apparatus according to claim 5, wherein thelight receiving unit is attached to the member and is sealed thereto. 7.A plasma processing apparatus according to claim 5, wherein the memberdisposed in the upper portion of the vacuum chamber is a member held tothe vacuum chamber.
 8. A plasma processing apparatus according to claim7, wherein the light receiving unit is attached to the member and issealed thereto.
 9. A plasma processing apparatus according to claim 5,wherein the member disposed in the upper portion of the vacuum chamberis a flat plate member which is disposed in parallel with the waferbeing opposed thereto.
 10. A plasma processing apparatus according toclaim 9, wherein the light receiving unit is attached to the member andis sealed thereto.
 11. A plasma processing apparatus according to claim9, wherein the member disposed in the upper portion of the vacuumchamber is a member held to the vacuum chamber.